You must consider several factors to ensure optimal server performance.
Each server application must have access to its designated storage with the following conditions:
High I/O rate (number of I/O operations per second)
High throughput (megabytes per second)
Minimal latency (response times)
Because each application has different requirements, you can meet these goals by choosing an appropriate RAID group on the storage system. To achieve performance goals, perform the following tasks:
Place each LUN on a RAID group that provides the necessary performance levels. Pay attention to the activities and resource utilization of other LUNS in the assigned RAID group. A high-performance RAID group that has too many applications doing I/O to it might not meet performance goals required by an application running on the ESXi host.
Provide each server with a sufficient number of network adapters or iSCSI hardware adapters to allow maximum throughput for all the applications hosted on the server for the peak period. I/O spread across multiple ports provides higher throughput and less latency for each application.
To provide redundancy for software iSCSI, make sure the initiator is connected to all network adapters used for iSCSI connectivity.
When allocating LUNs or RAID groups for ESXi systems, multiple operating systems use and share that resource. As a result, the performance required from each LUN in the storage subsystem can be much higher if you are working with ESXi systems than if you are using physical machines. For example, if you expect to run four I/O intensive applications, allocate four times the performance capacity for the ESXi LUNs.
When using multiple ESXi systems in conjunction with vCenter Server, the performance needed from the storage subsystem increases correspondingly.
The number of outstanding I/Os needed by applications running on an ESXi system should match the number of I/Os the SAN can handle.